Split biased radio frequency power amplifier with enhanced linearity

ABSTRACT

A radio frequency (RF) power amplifier (PA) may include a first transistor and a second transistor. A first power cell may be coupled with the first transistor, and a second power cell may be coupled with the second transistor. In embodiments, the first transistor may be scaled to operate at a first current density, while the second transistor may be scaled to operate at a second current density.

FIELD

Embodiments of the present disclosure generally relate to the field ofradio frequency (RF) power amplifiers (PAs).

BACKGROUND

For RF PAs used in wireless communication, linearity may be veryimportant. Generally, linearity may be a measure of how linear the RFsignal output of an RF PA is as the RF input signal is increased. Inother words, linearity may refer to the gain (sometimes referred to asAM-AM distortion wherein AM may refer to amplitude modulation) and phaseshift (sometimes referred to as AM-PM distortion wherein PM may refer tophase modulation) of the RF PA, and it may be desirable for the gain andphase to be consistent over a range of RF signal inputs or outputs suchthat the gain and phase of the RF PA at one signal input isapproximately the same as the gain and phase of the RF PA at anothersignal input. One of the key measurements of the RF PA linearity may bethe ACPR (Adjacent Channel Power Ratio), which may be the measure of theratio between the total adjacent channel power (sometimes referred to asan intermodulation signal) to the main channel's power (sometimesreferred to as a useful signal).

Existing RF PAs may include a bias circuit designed to bias the poweramplifier to improve linearity. The bias circuit may use a bipolartransistor, such as heterojunction bipolar transistor (HBT), a fieldeffect transistor such as a metal-oxide-semiconductor field effecttransistor (MOSFET), a metal-semiconductor field effect transistor(MESFET), a pseudomorphic high-electron mobility transistor (PHEMT), ora combination of the above such as a bipolar field effect transistor(BiFET) and/or a bipolar high-electron-mobility transistor (BiHEMT).However, regardless of the bias circuit, existing RF PAs may stillexhibit non-linear distortion in the output signal of the RF PA as theRF input signal of the RF PA increases.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be readily understood by the following detaileddescription in conjunction with the accompanying drawings. To facilitatethis description, like reference numerals designate like structuralelements. Embodiments are illustrated by way of example and not by wayof limitation in the figures of the accompanying drawings.

FIG. 1 schematically illustrates a circuit diagram of an RF PA,according to various embodiments.

FIG. 2 schematically illustrates a circuit diagram of an RF PA,according to various embodiments.

FIG. 3 illustrates a process of constructing an RF PA, according tovarious embodiments.

FIG. 4 is a simulated result of a first voltage compared against outputpower in an RF PA, according to various embodiments.

FIG. 5 is a simulated result of a second voltage compared against outputpower in an RF PA, according to various embodiments.

FIG. 6 is a simulated result of gain compared against output power fortwo different circuits, according to various embodiments.

FIG. 7 is a simulated result of adjacent channel power ratio (ACPR)compared against output power for two different circuits, according tovarious embodiments.

FIG. 8 schematically illustrates an example system including an RF PA,according to various embodiments.

FIG. 9 schematically illustrates a circuit diagram of an RF PA,according to various embodiments.

FIG. 10 is a simulated result of phase shift compared against outputpower for two different circuits, according to various embodiments.

DETAILED DESCRIPTION

Embodiments of the present disclosure provide techniques andconfigurations of an RF PA with increased RF signal linearity. Inembodiments, a first transistor may be coupled with a first power cell,and a second transistor may be coupled with a second power cell. Thefirst transistor and the second transistor may be scaled such that thesecond transistor may be much larger than the first transistor.Similarly, the first power cell and second power cell may be scaled suchthat the second power cell is much larger than the first power cell. Byconfiguring the RF PA in this manner, the output of the second powercell may be bias boosted such that the gain and phase of the RF PAexhibits an increased linearity response.

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, wherein like numeralsdesignate like parts throughout, and in which is shown by way ofillustration embodiments in which the subject matter of the presentdisclosure may be practiced. It is to be understood that otherembodiments may be utilized and structural or logical changes may bemade without departing from the scope of the present disclosure.Therefore, the following detailed description is not to be taken in alimiting sense, and the scope of embodiments is defined by the appendedclaims and their equivalents.

For the purposes of the present disclosure, the phrase “A and/or B”means (A), (B), or (A and B). For the purposes of the presentdisclosure, the phrase “A, B, and/or C” means (A), (B), (C), (A and B),(A and C), (B and C), or (A, B and C).

The description may use the phrases “in an embodiment,” or “inembodiments,” which may each refer to one or more of the same ordifferent embodiments. Furthermore, the terms “comprising,” “including,”“having,” and the like, as used with respect to embodiments of thepresent disclosure, are synonymous. The term “coupled” may refer to adirect connection, an indirect connection, or an indirect communication.

The term “coupled with,” along with its derivatives, may be used herein.“Coupled” may mean one or more of the following. “Coupled” may mean thattwo or more elements are in direct physical or electrical contact.However, “coupled” may also mean that two or more elements indirectlycontact each other, but yet still cooperate or interact with each other,and may mean that one or more other elements are coupled or connectedbetween the elements that are said to be coupled with each other.

As noted above, an RF PA may include one or more HBTs, BiFETs, BiHEMTs,MOSFETs, MESFETs, or PHEMTs. However, the RF PA may exhibit non-linearcharacteristics. FIG. 1 depicts an RF PA 100 that may exhibit increasedlinearity characteristics. In embodiments, the RF PA 100 may be coupledwith a power source 102 such as a battery or some other power sourcethat may provide a fixed reference voltage (V_(DD)) within the RF PA100. The RF PA 100 may include a first transistor 104 and a secondtransistor 106. As shown in FIG. 1, the gates of the first transistor104 and second transistor 106 may be coupled with one another. Inembodiments, the first transistor 104 and/or the second transistor 106may be MESFETs. Both the first transistor 104 and the second transistor106 may have a source terminal (designated in FIG. 1 with the letter“S”) and a drain terminal. As shown in FIG. 1, the drain terminals ofthe first transistor 104 and the second transistor 106 may be coupledwith one another. The gates of the first transistor 104 and the secondtransistor 106 may be coupled with the power source 102 through areference resistor 108. The source terminal of the first transistor 104may be coupled with the base terminal of a bipolar transistor 110 via afeedback resistor 112. Similarly, the gate terminals of the first andsecond transistors 104 and 106 may be coupled with the collectorterminal of the bipolar transistor. In some embodiments, the bipolartransistor 110 may be a heterojunction bipolar transistor. In someembodiments, the bipolar transistor 110 may be a BiFET or BiHEMTtransistor, as shown. In other embodiments, not shown in FIG. 1, thebipolar transistor 110 may not be bipolar, but instead may be a MOSFET,MESFET, or PHEMT transistor. The emitter terminal of the bipolartransistor 110 may be coupled with ground, as shown in FIG. 1.

In embodiments, the source terminal of the first transistor 104 may becoupled with a first power cell 114 via a first line 116. The firstpower cell 114 may be indicated by the dashed line, as shown in FIG. 1.In embodiments, the first power cell 114 may include a first power cellstructure including a first resistor 118 and a first capacitor 120coupled with the base terminal of a first bipolar transistor 122, asshown in FIG. 1. In some embodiments, the first bipolar transistor 122may be a heterojunction bipolar transistor. In some embodiments, thefirst bipolar transistor 122 may be a BiFET or BiHEMT.

The source terminal of the second transistor 106 may be coupled with asecond power cell 124 via a second line 126. The second power cell 124may be indicated by the dashed line in FIG. 1. In embodiments, thesecond power cell 124 may include a plurality of power cell structuressimilar to those of the first power cell 114. Specifically, the secondpower cell 124 may include a second power cell structure 128 including asecond resistor 130, a second capacitor 132, and a second bipolartransistor 134. The second power cell 124 may additionally include oneor more other power cell structures such as third power cell structure136. In some embodiments, the second power cell 124 may have up tofifteen power cell structures, as indicated by the dashed lines in FIG.1 and fifteenth power cell structure 138. In some embodiments, thesecond bipolar transistor 134 may be a heterojunction bipolartransistor. In some embodiments, the second bipolar transistor 134 maybe a BiFET or BiHEMT. In some embodiments, the first power cell 114 mayhave an increased number of power cell structures. In some embodiments,the second power cell 124 may have more or less than fifteen power cellstructures.

In embodiments, the resistors of each of the power cell structures 128,136 and 138 in the second power cell 124 may be coupled with the sourceterminal of the second transistor 106 via the second line 126. Inembodiments, the emitters of each of the bipolar transistors in thesecond power cell 124, for example second bipolar transistor 134, may becoupled with one another and to ground via an emitter-ground line 140.As shown, the emitter of the first bipolar transistor 122 in the firstpower cell 114 may likewise be coupled with ground.

The collectors of each of the bipolar transistors in the second powercell 124, for example second bipolar transistor 134, may be coupled withone another and to the collector of the first bipolar transistor 122 inthe first power cell 114 via the first collector line 142. Similarly,the capacitors of each power cell structure, for example first capacitor120 of the first power cell 114 and second capacitor 132 of the secondpower cell 124, may be coupled with one another via a third power line144.

The third power line 144 may be coupled with an RF input 146 configuredto provide an input voltage or power to the RF PA 100. The firstcollector line 142 may be coupled with an operating power or voltageinput 148 configured to provide an operating voltage to the RF PA 100.In embodiments, the operating power input 148 may be coupled with aninductor 150. In some embodiments, the first collector line may also becoupled with RF output power 152. In some embodiments, RF output power152 may be coupled with a matching network (not shown).

The RF PA 100 depicted in FIG. 1 exhibits increased linearity over otherexisting RF PAs. Specifically, the use of both the first transistor 104and the second transistor 106 may be considered to split the MOSFET,MESFET, PHEMT, BiFET or BiHEMT of an existing RF PA into twotransistors. The device size of the first transistor 104 may be smallerthan the second transistor 106. For example, in one embodiment thedevice size of the first transistor 104 may be on the order of 40 um²,and the device size of the second transistor 106 may be on the order of1200 um². The result of this difference may be that the first transistor104 may be scaled to work at a relatively high current density, and thesecond transistor 106 may be scaled to work at a relatively low currentdensity. Current density may be defined as the current pass through thetransistor divided by the device size of that transistor.

In embodiments, scaling the first transistor 104 and the secondtransistor 106 to work at different current densities may involveselecting the ratio of the device size of the first transistor 104 andthe second transistor 106, and the ratio of the power cell size of thefirst power cell 114 and the second power cell 124. If the ratio of thedevice size of the first transistor 104 and the second transistor 106 isdifferent from the ratio of the power cell size of the first power cell114 and the second power cell 124, then the first transistor 104 and thesecond transistor 106 may be said to work at different currentdensities.

Additionally, the RF power cells of existing RF PAs may be split intotwo parts, the first power cell 114 and the second power cell 124. Ascan be seen in FIG. 1, the first power cell 114 may be smaller than thesecond power cell 124. For example, the first power cell 114 may onlycontain a single power cell structure, while the second power cell 124may contain a plurality of power cell structures. As noted, the secondpower cell 124 may contain as many as fifteen power cell structures insome embodiments, while in other embodiments the second power cell 124may include more or less power cell structures.

In embodiments, the reference resistor 108 may serve to set a referencecurrent to the collector of the bipolar transistor 110. Additionally,the feedback resistor 112 may sense a voltage change in the first line116. The voltage of the first line 116 may be described as V_(b1). Thevoltage of the second line 126 may be described as V_(b2).

As can be seen in FIG. 1, the first power cell 114, the feedbackresistor 112, bipolar transistor 110, and the first transistor 104 mayform a PA with a closed loop bias circuit as a current mirror. In otherwords, the quiescent current of transistor 112 may be set by thereference current at the collector of transistor 110, which may be thesame current pass through the resistor 108. By contrast, the secondpower cell 124, and the second transistor 106 may form a PA with an openloop bias circuit. In other words, the quiescent current of transistorsin power cell 124 may not be directly set by the reference current atthe collector of transistor 110. Instead, the quiescent current oftransistors in power cell 124 may be set by the current passing throughthe transistor 106 directly. Because the respective gates of transistor104 and transistor 106 may be coupled; the gate voltage of thetransistor 106 may be the same voltage of the gate voltage of transistor104, which may be set by the close loop current mirror bias describedabove. The source terminal voltage of the transistor 106 may be close tothe base emitter junction voltage V_(be) of the transistor in the powercell 124 (for example the transistor 134). Additionally, the baseemitter junction voltage V_(be) of the power cell 124 may be very closeto the base emitter junction voltage V_(be) of the transistor 122 in thepower cell 114 because transistor 134 and transistor 122 may be the sametype of bipolar transistor with the same process. Because the gatevoltages of transistor 104 and transistor 106 may be the same, and thesource voltages of transistor 104 and transistor 106 may be the same orvery close, then the ratio of the current passing through the transistor106 and the current passing through the transistor 104 may be closelyproportional to the device size of the transistor 106 and the transistor104 if the change of the source terminal voltage of the transistor 106with current passing though it is not considered. The current density ofthe transistor 104 and transistor 106 may therefore be the same in thiscase.

However, the current passing through transistor 106 may cause adifferent source terminal voltage at transistor 106 as compared withtransistor 104 when the size of transistor 104 transistor 106, and thesize of power cell 124 and power cell 114 are scaled. In turn, thedifferent source terminal voltage of transistor 106 may change thecurrent passing though the transistor 106 as well as the current densityof the transistor 106.

For example, if the device size ratio of transistor 104 and transistor106 is approximately 1:30, the current passing through the transistor106 may be approximately 30 times the current passing through transistor104 because the source terminal voltage of transistor 104 and transistor106 may be close to one another. Also, if the size of the power cell 124is scaled to be approximately 15 times the size of power cell 114, thenthe current passing through the base of each transistor of power cell124 may be about twice the current passing through the base of thetransistor of power cell 114.

Additionally, there may be a base ballasting resistor of the same valueat the base of each transistor, for example resistor 118 and resistor130. So the voltage drop across the base ballasting resistor of powercell 124 may be about twice that of power cell 114. As described above,the base emitter junction voltage V_(be) of the transistor of power cell114 and power cell 124 may be the same due to the same process of thesame type of transistors. The higher voltage drop on the base ballastingresistors of the power cell 124 may cause the source terminal voltage ofthe transistor 106 to be higher than that of transistor 104. The highersource terminal voltage may cause the actual current passing through thetransistor 106 to be less than twice the current passing through thetransistor 106, even though the size of the transistor 106 may still betwice the size of the transistor 104, as discussed above, when the gatevoltage and the transistor type are the same.

Therefore, in this example, the transistor 106 may have a lower currentdensity than the transistor 104. In other examples, different ratios oftransistor 104 and transistor 106 may result in different currentpassing through the transistor 106 with different current density. Ingeneral, when the device size of transistor 104 and transistor 106 arescaled, and the device size of power cell 114 and power cell 124 arescaled, the current density of transistor 104 and transistor 106 may becontrolled.

In operation, as the RF input signal provided by RF input 146 increases,the voltage of the first line 116 may drop. Generally the voltage of thesecond line 126 may have a tendency to also drop. The voltage drop ofthe first line 116 and the second line 126 may cause the bias points ofthe first power cell 114 and the second power cell 124 to drop with theincrease of the input power at the RF input 146. However, when thevoltage of the first line 116 drops, the current to the base of thebipolar transistor 110 may also drop. The drop in the current to thebase of the bipolar transistor 110 may cause the current of thecollector terminal of the bipolar transistor 110 to drop as well. As canbe seen, the current at the collector terminal of the bipolar transistor110 may be the same current that passes through the reference resistor108, so the voltage drop across the reference resistor 108 may decrease.

As noted earlier, the power source 102 may provide a fixed referencevoltage, V_(DD). In embodiments, V_(DD) may be considered to begenerated externally to the RF PA 100. As noted above, an increase inthe RF input signal provided by RF input 146 may result in a decreasedvoltage drop across reference resistor 108. Because V_(DD) is a fixedvoltage, the decrease of the voltage drop across the reference resistor108 may result in a voltage increase at the gate terminals of the firsttransistor 104 and the second transistor 106.

As noted above, the first transistor 104 and second transistor 106 maybe scaled to work at different current densities. Specifically, thefirst transistor 104 may be scaled to work at a higher current densitywhile the second transistor 106 is scaled to work at a lower currentdensity when the quiescent working point is selected. Because of thecurrent density difference, the voltage across the gate terminal and thesource terminal of the first transistor 104 may be greater than thevoltage across the gate terminal and the source terminal of the secondtransistor 106. Because the gates of the first transistor 104 and secondtransistor 106 are electrically coupled, this voltage difference maypull the voltage of the second line 126 higher than the voltage of thefirst line 116. Pulling the voltage of the second line 126 higher thanthe voltage of the first line 116 may cancel the above describedtendency for the voltage of the second line 126 to drop.

This increased voltage in the second line 126 may be controlled orscaled by properly adjusting the device size of the first transistor 104or the second transistor 106. Similarly, adjusting the scale or size ofcomponents of the first power cell, for example first bipolar transistor122, or the scale and/or size of components of the second power cell,for example second bipolar transistor 134, may likewise affect theincreased voltage in the second line 126. Additionally, adjusting theratio of the number of power cell structures in the first power cell 114or the second power cell 124 may likewise affect the increased voltagein the second line 126. In embodiments, the first transistor 104, secondtransistor 106, first power cell 114, and/or second power cell 124 maybe selected to provide a desired voltage change of the second line 126with an RF input signal power increase from the RF input 146. Inembodiments, providing the desired voltage change of the second line 126may cause the voltage of the second line 126 to remain approximately thesame regardless of an increase in RF input signal power from the RFinput 146. In other embodiments, providing the desired voltage change ofthe second line 126 may cause the voltage of the second line 126 toincrease as the RF input signal power from the RF input 146 increases,which may be called “bias boosting.” As described below with respect toFIGS. 4 and 5, the desired voltage change of the second line 126 mayoccur when the voltage of the second line 126 increases slightly as theRF input signal power increases from the RF input 146.

As used herein, signal power or power may refer to a measurement inunits of watts, milliwatts, dBm or some other power measurement. Changesto signal power may refer to changes in milliwatts or some other unit.In other embodiments, changes to signal power may refer to changes involtage and/or current.

In general, it may be seen that the second line 126 may provide the biascurrent for the second power cell 124, which may be significantly largerthan the first power cell 114 as described above. Because the secondpower cell 124 may be significantly larger than the first power cell114, the second power cell 124 may amplify the majority of the RF inputsignal for the RF PA 100. Therefore, even though the voltage of thefirst line 116 may decrease as the RF input signal power increases, theoverall linearity of the RF PA 100 may improve due to bias boostingeffect on the second line 126.

FIG. 2 depicts an RF PA 200 which may be similar to the RF PA 100 ofFIG. 1. The primary difference between the RF PA 100 of FIG. 1 and theRF PA 200 of FIG. 2 may be that the first transistor 204 may be abipolar transistor rather than a MESFET type transistor. Similarly, thesecond transistor 206 of the RF PA 200 of FIG. 2 may be a bipolartransistor. In other embodiments, a first transistor of an RF PA, forexample first transistors 104 or 204, may be a MESFET type transistorwhile the second transistor of the RF PA, for example second transistors106 or 206, may be a bipolar type transistor (or vice versa). In otherembodiments, one or both of the first transistor and second transistorof an RF PA may be a metal-oxide-semiconductor field-effect transistor(MOSFET) or some other type of field effect transistor (FET) or someother type of bipolar transistor.

As shown in FIG. 2, the emitter terminal of the first transistor 204 maybe coupled with a first line 216, which in turn may be coupled with afirst power cell 214. Similarly, the emitter terminal of the secondtransistor 206 may be coupled with a second line 226, which may in turnbe coupled with a second power cell 224.

FIG. 9 depicts an RF PA 900 which may be similar to the RF PA 100 ofFIG. 1 or the RF PA 200 of FIG. 2. However, in RF PA 900, thetransistors of the first power cell 914 and the second power cell 924may not be bipolar transistors, but may be a different type oftransistor such as a MOSFET, MESFET, PHEMT, or some other type oftransistor. Specifically, the first transistor 922 and the secondtransistor 934 may be non-bipolar transistors and may instead be aMOSFET, MESFET, or PHEMT. Similarly, the transistors of the third powercell structure 936 through the fifteenth power cell structure 938 maynot be bipolar transistors. As shown in FIG. 9, the first transistor904, the second transistor 906 and reference transistor 910 may not bebipolar transistors, but may be a different type of transistor such as aMOSFET, MESFET, PHEMT, or some other type of transistor.

It will be understood that the RF PAs 100, 200, and 900 are examples ofdifferent embodiments, and in other embodiments different transistorsmay be bipolar or non-bipolar transistors. For example, in someembodiments, the transistors of the first and second power cells may bebipolar transistors while the first and second transistors arenon-bipolar transistors. In some embodiments the reference transistormay be bipolar, for example bipolar transistor 110, or non-bipolar, forexample reference transistor 910.

FIG. 3 depicts an example process 300 for constructing an RF PA such asRF PAs 100, 200, or 900. In embodiments, a first transistor, for examplefirst transistor 104, 204, or 904, may be coupled with a current/voltagesource, for example power source 102, 202, or 902 at 302. A secondtransistor, for example second transistor 106, 206, or 906, may then becoupled with the current/voltage source at 304. The first transistor maythen be coupled with the second transistor at 306. For example, as shownin FIG. 1, 2, or 9, the gates or base of the first transistor and secondtransistor may be coupled with one another. Alternatively, the collectorterminals and/or drain terminals may be coupled with one another.

The first transistor may then be coupled with a first power cell, forexample first power cell 114, 214, or 914, at 308. Similarly, the secondtransistor may be coupled with a second power cell, for example secondpower cell 124, 224, or 924 at 310.

Various operations are described as multiple discrete operations inturn, in a manner that is most helpful in understanding the claimedsubject matter. However, the order of description should not beconstrued as to imply that these operations are necessarily orderdependent. In particular, these operations may not be performed in theorder of presentation. Operations described may be performed in adifferent order than the described embodiment. Various additionaloperations may be performed and/or described operations may be omittedin additional embodiments.

FIGS. 4 and 5 depict a simulated result of increasing the RF outputsignal power due to increased RF input signal power for an RF PA such asRF PA 100. Specifically, FIG. 4 depicts a simulated voltage at the firstline 116 as the RF output signal power is increased, for example byincreasing the RF input signal power at the RF input 146 and amplifyingit using the RF PA 100. By contrast, FIG. 5 depicts a simulated voltageat the second line 126 as the RF output signal power is increased. Ascan be seen in FIG. 4, the voltage of the first line may stay relativelylevel until an output signal power between 25 and 30 dBm (sometimesreferred to as dBmW), at which point the voltage of the first line maystart to decrease significantly. By contrast, as can be seen in FIG. 5,the voltage of the second line may increase slightly as the outputsignal power increases until the output signal power reaches roughly 33dBm, at which point the voltage of the second line may increasesignificantly. These inflection points where the voltages of the firstor second lines begin to change more dramatically may be based on one ormore of the particular values or scales associated with the firsttransistor 104, the second transistor 106, the first power cell 114,and/or the second power cell 124. It may also be seen in FIG. 5 that thevoltage of the second line may increase slightly as the output signalpower increases until the output signal power reaches an inflectionpoint at roughly 33 dBm. This increase in the voltage of the second linemay be based on the bias boosting effect described above with respect toFIG. 1. As noted, the simulated results of FIGS. 4 and 5 are merelyexamples, and in other embodiments the values used may be different dueto a difference in one or more of the first transistor 104, the secondtransistor 106, the first power cell 114, and/or the second power cell124.

FIG. 6 may depict a simulated result of increasing RF output signalpower in an RF PA. Specifically, FIG. 6 may depict a simulatedcomparison of signal gain in an RF PA against output signal power for anexisting circuit and an RF PA such as RF PA 100. The first line 600 maydepict output signal gain of an existing RF PA compared against outputsignal power in dBm of the existing RF PA. By contrast, the second line605 may depict output signal gain of an RF PA such as RF PA 100 comparedagainst output signal power in dBm of an RF PA such as RF PA 100. InFIG. 6, an existing RF PA may have a relatively linear signal gain whenoutput signal power is between from 17 dBm through 21 dBm, at whichpoint the existing RF PA may start to exhibit non-linearcharacteristics. Specifically, after an output signal power ofapproximately 21 dBm, the signal gain may vary as the output signalpower increases. The non-linear signal gain characteristics may increaseas output signal power increases to approximately 31 dBm, at which pointthe RF PA may exhibit significant non-linear signal gaincharacteristics. That is, the signal gain may vary significantly as theoutput signal power increases.

By contrast, the RF PA of the present disclosure, for example RF PA 100,may exhibit strong linear gain characteristics as output signal powerincreases from 17 dBm through 25 dBm, that is the signal gain at a firstoutput signal power may be approximately similar to the signal gain atanother output signal power. As the output signal power reaches andpasses approximately 25 dBm, the RF PA such as RF PA 100 may start toexhibit slight non-linear signal gain characteristics. Therefore, as canbe seen in FIG. 6, the RF PA of the present disclosure may exhibitsignificantly increased linear characteristics.

FIG. 10 may depict a simulated result of increasing RF output signalpower in an RF PA according to the present disclosure. Specifically,FIG. 10 may depict a simulated comparison of signal phase shift in an RFPA against output signal power for an existing circuit, line 1000 and anRF PA such as RF PA 100, 200, or 900, line 1005. As shown in FIG. 10,the phase of an RF PA according to the present disclosure, line 1005,may be significantly smaller than that of an existing RF PA as shown atline 1000 FIG. 7 depicts a simulated comparison of ACPR of an existingcircuit and an RF PA such as RF PA 100 to output signal power of therespective circuits. Specifically, the first line 700 may represent theACPR of an existing circuit compared to the output signal power of thatcircuit. The second line 705 may represent the ACPR of an RF PA such asRF PA 100 to the output signal power of the RF PA. In embodiments, itmay be desirable for ACPR to remain low as output signal powerincreases. Particularly, for example in EDGE communicate standard, itmay be desirable for the ACPR to remain generally below −57 dBc(represented by the horizontal dashed line in FIG. 7) as output signalpower increases up to an output power of the PA of between 29 and 30 dBm(represented by the vertical dashed line in FIG. 7). This relatively lowACPR may be desirable because the low ACPR may result in lessinterference to the user at adjacent channel. As can be seen in FIG. 7,the ACPR of an existing circuit may be above the desired ACPR at anoutput signal power of between 29 and 30 dBm. By contrast, the ACPR ofthe RF PA such as RF PA 100 may remain below the ACPR threshold of −57dBc until the output signal power of the RF PA reaches approximately31.5 dBm. It will be understood that these examples are simulatedresults for one embodiment of an RF PA such as RF PA 100 and an existingRF PA. In other embodiments the different ACPR slopes or intercepts oflines 700 or 705 may be different. Additionally, the threshold values ofapproximately −57 dBc for ACPR and 29.7 dBm for output power may bedifferent in other embodiments.

Embodiments of an RF PA (e.g., the RF PAs 100 or 200) described herein,and apparatuses including such RF PA may be incorporated into variousother apparatuses and systems. A block diagram of an example system 800is illustrated in FIG. 8. As illustrated, the system 800 includes a PAmodule 802, which may be an RF PA module in some embodiments. The system800 may include a transceiver 804 coupled with the PA module 802 asillustrated. The PA module 802 may include one or more RF PAs (e.g., theRF PAs 100 or 200) described herein.

The PA module 802 may receive an RF input signal, RFin, from thetransceiver 804. The PA module 802 may amplify the RF input signal,RFin, to provide the RF output signal, RFout. The RF input signal, RFin,and the RF output signal, RFout, may both be part of a transmit chain,respectively noted by Tx-RFin and Tx-RFout in FIG. 8.

The amplified RF output signal, RFout, may be provided to an antennaswitch module (ASM) 806, which effectuates an over-the-air (OTA)transmission of the RF output signal, RFout, via an antenna structure808. The ASM 806 may also receive RF signals via the antenna structure808 and couple the received RF signals, Rx, to the transceiver 804 alonga receive chain.

In various embodiments, the antenna structure 808 may include one ormore directional and/or omnidirectional antennas, including, e.g., adipole antenna, a monopole antenna, a patch antenna, a loop antenna, amicrostrip antenna or any other type of antenna suitable for OTAtransmission/reception of RF signals.

The system 800 may be any system including power amplification. The RFPA (e.g., RF PAs 100 or 200) may provide an effective switch device forpower-switch applications, which may include power conditioningapplications, such as, for example, Alternating Current (AC)-DirectCurrent (DC) converters, DC-DC converters, DC-AC converters, and thelike. In various embodiments, the system 800 may be particularly usefulfor power amplification at high radio frequency power and frequency. Forexample, the system 800 may be suitable for any one or more ofterrestrial and satellite communications, radar systems, and possibly invarious industrial and medical applications. More specifically, invarious embodiments, the system 800 may be a selected one of a radardevice, a satellite communication device, a mobile handset, a cellulartelephone base station, a broadcast radio, or a television amplifiersystem.

Although certain embodiments have been illustrated and described hereinfor purposes of description, a wide variety of alternate and/orequivalent embodiments or implementations calculated to achieve the samepurposes may be substituted for the embodiments shown and describedwithout departing from the scope of the present disclosure. Thisapplication is intended to cover any adaptations or variations of theembodiments discussed herein. Therefore, it is manifestly intended thatembodiments described herein be limited only by the claims and theequivalents thereof.

What is claimed is:
 1. A power amplifier comprising: a first transistorscaled to operate at a first current density; a second transistor scaledto operate at a second current density, the first transistor coupledwith the second transistor; a first power cell comprising a thirdtransistor coupled with the first transistor, the first transistorconfigured to bias the first power cell; and a second power cellcomprising a plurality of transistors coupled with the secondtransistor, the second transistor configured to bias the second powercell; wherein the third transistor includes a first collector, andindividual transistors in the plurality of transistors includerespective collectors, and the first collector is coupled with therespective collectors.
 2. The power amplifier of claim 1, wherein thefirst transistor is a bipolar transistor.
 3. The power amplifier ofclaim 2, wherein the first transistor includes a first base; and whereinthe second transistor is a bipolar transistor that includes a secondbase coupled with the first base.
 4. The power amplifier of claim 1,wherein the first transistor is a field-effect transistor.
 5. The poweramplifier of claim 4, wherein the first transistor includes a firstgate; and wherein the second transistor is a field-effect transistorthat includes a second gate coupled with the first gate.
 6. The poweramplifier of claim 1, wherein the plurality of transistors comprisefifteen transistors.
 7. A method comprising: coupling an input of afirst transistor to a power source, the first transistor scaled based ona first current density; coupling an input of a second transistor to thepower source, the second transistor scaled based on a second current;coupling a first terminal of the first transistor with a first terminalof the second transistor; coupling an input of a first power cellincluding a third transistor with a second terminal of the firsttransistor; and coupling an input of a second power cell including aplurality of transistors with a second terminal of the secondtransistor; wherein the third transistor includes a first collector, andeach transistor in the plurality of transistors respectively includerespective collectors, and further comprising coupling the firstcollector with the respective collectors.
 8. The method of claim 7,wherein the first transistor is a bipolar transistor.
 9. The method ofclaim 8, wherein the input of the first transistor is a first base;wherein the second transistor is a bipolar transistor; and wherein theinput of the second transistor is a second base.
 10. The method of claim7, wherein the first transistor is a field-effect transistor.
 11. Themethod of claim 10, wherein the input of the first transistor is a firstgate; wherein the second transistor is a field-effect transistor; andwherein the input of the second transistor is a second gate.
 12. Themethod of claim 7, wherein the plurality of transistors comprise fifteentransistors.
 13. A system comprising: a power source; and a poweramplifier coupled with the power source, wherein the power amplifierincludes: a first transistor scaled to operate at a first currentdensity, the first transistor coupled with the power source; a secondtransistor scaled to operate at a second current, the first transistorcoupled with the power source; a first power cell comprising a thirdtransistor coupled with the first transistor; and a second power cellcomprising a plurality of transistors coupled with the secondtransistor; wherein the third transistor includes a first collector, andeach transistor in the plurality of transistors respectively includerespective collectors, and the first collector is coupled with therespective collectors.
 14. The system of claim 13, wherein the firsttransistor is a bipolar transistor.
 15. The system of claim 14, whereinthe first transistor includes a first base and wherein the secondtransistor is a bipolar transistor that includes a second base coupledwith the first base.
 16. The system of claim 13, wherein the firsttransistor is a field-effect transistor.
 17. The system of claim 16,wherein the first transistor includes a first gate and wherein thesecond transistor is a field-effect transistor that includes a secondgate coupled with the first gate.
 18. The system of claim 13, whereinthe plurality of transistors comprise fifteen transistors.
 19. Thesystem of claim 13, further comprising a transceiver coupled with thepower amplifier.